fix(audit): reference catalogs and pointers are not governance documents (0.1.0-alpha.13) - #43

Validation Date Coverage asked every canonical governance file for a
`Last validated:` line. Two document kinds were never governance documents:

- `docs/patterns/**` — a reference catalog read on demand. lc-classic-starter
  sat CRITICAL at 22% coverage, and 7 of its 9 governance files were catalog
  entries. Stamping ~20 of them changes no agent behaviour.
- pointer documents — already named by isPointerDocument, which this check did
  not consult.

Both leave the denominator rather than being counted and forgiven, and the
exemption is stated in the check detail so a coverage figure that rose stays
auditable: "100% ... (excludes 7 reference/pointer docs)". Scoped to this one
coverage figure — both kinds remain on the scoring surface for every other
check, exactly as the shim exclusion in #41 was scoped to Low-Yield.

Two mistakes of mine are worth recording, because both were caught by the
harness rather than by me:

I also exempted `docs/bootstrap-templates/**`, which the brief never asked for.
Anvil's own governance surface is 18 bootstrap templates, all dated, so the
exemption emptied its denominator and an empty denominator read as 0% — turning
Anvil's own verdict from PASS to CRITICAL. verify:self-audit-proof caught it,
one turn after I loosened that proof's PR-churn normalization, which is decent
evidence the loosening did not blind it. Templates are now treated as the
governance documents they are.

The empty-denominator case is guarded separately: when every governance file is
exempt there is nothing left to measure, so the check falls back to the full set
rather than inventing a 0%.

Fleet sweep across 17 repos, before -> after: exactly one verdict moves,
lc-classic-starter CRITICAL -> NEEDS WORK. Nothing else shifts. forge stays
CRITICAL correctly — after exempting its 3 catalog entries, its two remaining
`.devagent` files are ordinary instruction docs that genuinely carry no date.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>